Changes between Version 1 and Version 2 of binder_ew

05/04/12 11:02:03 (9 years ago)



  • binder_ew

    v1 v2  
    26263. What's the velocity structure like?   
    28 1. P-wave arrivals: 
     28'''1. P-wave arrivals:''' 
    3030Two commands in binder's configuration file tell it where it should get the P-wave arrivals to work on.  The "RingName" command specifies which Earthworm transport ring (a shared memory region) to read from.  Make sure that this is the same ring into which pick_ew is writing its output.  Also, if you're importing picks from another source and want binder to use them, make sure you are placing them in this ring as well.  
    3232The "GetPicksFrom" command specifies the installation id and module id of the TYPE_PICK2K messages that binder will operate on.  Specific id's or wildcards can be used for either or both of these arguments.  Note: both binder_ew and eqproc should be set to listen to the same pick source(s)! 
    34 2. Station List: 
     34'''2. Station List:''' 
    3636Binder expects the network's station list to be in a file in Hypoinverse station format; it gets the name of the file from the "site_file" command. Of all the fields in this file, the only ones used by binder are the station codes (5-letter site code, 2-letter network code, 3-letter component code) and the station  latitude and longitude.  A quirk of this file is that all lats and lons are listed as positive numbers; a letter is used to denote N,S,E,W, with blanks interpreted as N and W.  As binder reads the file, it converts lat and lon to decimal degrees with N and E being positive.  If a site has multiple components, each component should be listed on its own line in the station file. As of Earthworm v4.0, binder treats each component independently, so if multiple components at a site are picked, that site will be weighted more heavily in stacks and locations than a single-component site. 
    4040Since binder works only on arrival times, it doesn't need to know anything about instrument response or gain. 
    42 3. Velocity Model: 
     42'''3. Velocity Model:''' 
    4444Binder uses one simple velocity model to calculate travel times for the entire region of interest.  If the velocity structure varies greatly in your region, make sure you give binder a decent average model.  This velocity model is specified with a series of "lay" commands in the configuration file, listed in order of  increasing depth.  The velocities in each layer are constant, and should increase with depth (no low velocity zones, please).  Pay attention to the order of the arguments of the lay command.  It should be "lay depth(km) velocity(km/s)".  If you get depth and velocity swapped, binder won't do much of anything. 
    62 Stacking Grid Boundaries: 
     62'''Stacking Grid Boundaries:''' 
    6464The boundaries of the stacking grid are set with three commands: 
    6868Reviewing the map of historic seismicity may help in setting the stacking grid boundaries.  Binder can only identify new hypocenters that lie within these boundaries, so they should include the entire volume of interest (ie, wherever you expect or hope to see earthquakes).  Also, all of your seismic stations should lie within the grid boundaries. 
    70 Stacking Grid Cell Size: 
     70'''Stacking Grid Cell Size:''' 
    7272Now you must decide how big each cell within the grid will be. Each cell is a cube, and its side-length (in kilometers) is set with the "dspace" command. That map may be useful again; hopefully, you can set dspace so that only one station falls within each grid cell. The more stations that fall within one cell, the more trouble binder will have in "focusing" the stack (when 2 stations are in the same grid cell, their "hollyhocks" will overlap 100%, which doesn't do much good for resolving potential hypocenters). Then again, you don't want to make the cell size too small, or binder will have a lot more computations to do.  So there's a tradeoff here.  FYI, the Northern California Seismic Network uses a grid cell size of 4 km. 
    74 Stacking Distance Constraints: 
     74'''Stacking Distance Constraints:''' 
    7676When stacking each additional pick, binder considers possible hypocenters for that arrival within a limited distance of the station, not the entire stacking grid.  The stacking distance is controlled by the "rstack" command. Binder computes each pick's "hollyhock" within its stacking volume. The stacking volume includes the entire depth range of the stacking grid, but in map view the stacking volume is a square centered on the station location, extending rstack kilometers in each horizontal direction (the square's sides are 2*rstack km long). To avoid roundoff problems, rstack should be a multiple of the grid-cell dimension, dspace. 
    8181But, you have to stack it first! 
    83 Stacking and Time Resolution: 
     83'''Stacking and Time Resolution:''' 
    8585Binder includes a time-resolution factor ("tstack" command) in calculating the set of all possible hypocenters ("the hollyhock") for each pick.  This time factor controls the thickness of the hollyhock petals. Increasing tstack could increase the number of grid cells each pick's hollyhock. As a first approximation, tstack should be at least the number of seconds it takes for a P-wave to cross a grid cell of dspace km. 
    87 Pre-Stack Glitch Filtering: 
     87'''Pre-Stack Glitch Filtering:''' 
    8989A glitch is a group of coincident arrivals often caused by noisy telemetry. For the purposes of this filter, a glitch is defined as a certain number of picks (m) occurring in a given number of seconds (x). The values of both m and x are configurable with the "define_glitch" command (the default definition is 4 picks within 0.035 seconds).  This glitch filter was added to the stacking portion of binder to prevent it from creating new events from a group of picks having nearly identical arrival times. Picks that are flagged as belonging to a "glitch" are not used in summing the stack, but may later be associated with an event.  If you want to turn off pre-stack glitch filtering (ie, to make binder stack every pick), set m to zero (example "define_glitch 0 0.0"). 
    91 Summing the Stack - Stacking Weights & Event Thresholds: 
     91'''Summing the Stack - Stacking Weights & Event Thresholds:''' 
    9393OK, here we go. Binder gets a new pick and it doesn't associate with any 
    152152distant events. 
    154 Stacking and Eventids: 
     154'''Stacking and Eventids:''' 
    155156  Every time binder identifies a new event with a stack, it assigns 
    156157an eventid to it.  Binder uses this eventid in its internal bookkeeping 
    178 Associating New Phases with Active Earthquakes 
    179 ---------------------------------------------- 
     179=== Associating New Phases with Active Earthquakes === 
    180180  Whenever binder retreives a new pick, the first thing it does is try 
    181181to associate the arrival time with one of its currently active earthquakes. 
    195195the initiating pick (see stacking section above). 
    197 Association and Time Constraints: 
    198   As I mentioned above, binder keeps track of the 100 most recent hypocenters. 
     197'''Association and Time Constraints''' 
     198As I mentioned above, binder keeps track of the 100 most recent hypocenters. 
    199199When it tries to associate a new pick, it doesn't actually consider all of 
    200200those hypocenters as possible sources for the pick.  Instead, it considers 
    205205binder will not attempt to associate that pick with that event. 
    207 Association and Distance Constraints: 
     207'''Association and Distance Constraints''' 
    208209   Binder keeps track of the average epicentral distance (rAvg) of all phases 
    209210associated with each active hypocenter in its list. Before binder attempts 
    226227or restpr) for a pick to be associated with a given active hypocenter is 
    227228composed of three terms: 
    229230   restpr = dist-taper + res1_OT + res2_OT 
    231232The first term (dist-taper) is based on the distance of the current pick to 
    232233the hypocenter (controlled with the "taper" commands) and two remaining 
    236237for more poorly located earthquakes. 
    238 Residual Tolerance Distance Term, dist-taper: 
     239'''Residual Tolerance Distance Term, dist-taper''' 
    239241  The distance-dependent term of residual tolerance, dist-taper, is controlled 
    240242with the "taper r resmax" command, where r is the epicentral distance (km) and 
    252254factor in the "Relocation and Pick Weighting" section below). 
    254 Residual Tolerance Hypocentral Quality Terms, res1_OT and res2_OT: 
     256'''Residual Tolerance Hypocentral Quality Terms, res1_OT and res2_OT''' 
    255257  The "taper_OT OTconst1 OTconst2" sets two constants that are used to 
    256258calculate the hypocenter-quality terms of the maximum-allowed travel-time 
    264266associated with the event.  Binder uses the first constant, OTconst1, in 
    265267calculating res1_OT for each hypocenter as follows: 
    267269   res1_OT = OTconst1 * rms * Npick_factor 
    269271   where  Npick_factor = 3.0                     when npick <= 4 
    270272                       = SQRT( npick/(npick-4) ) when npick  > 4 
    272274When the number of picks is small, the rms of the location is often quite 
    273275low, so the Npick_factor and OTconst1 will dominate the res1_OT term. 
    279281station and the second constant, OTconst2.  Given the hypocentral (slant) 
    280282distance to the nearest station calculated by: 
    282284   s = SQRT( z**2 + dmin**2 )  where    z = hypocentral depth 
    283285                                     dmin = epicentral distance to 
    284286                                            nearest station 
    286288binder calculates the res2_OT tolerance term as follows: 
    288290   res2_OT = 0.0                     when s  < 1.0 
    289291           = OTconst2 * log10( s )   when s >= 1.0 
    291293The larger the minimum slant distance, the more unreliable the location, 
    292294and the larger this second residual taper term becomes. 
    304 Binder's Simple Event Locator 
    305 ----------------------------- 
     306=== Binder's Simple Event Locator === 
    306308  After binder declares a new event from a stack, or after is associates 
    307309a new pick with an active event, it passes the event to its simple L1 locator 
    312314locator, and I'll describe them below. 
    314 Intermittent Relocation: 
     316'''Intermittent Relocation''' 
    315317  While binder's locator is simple, it can still be quite a CPU hog, especially 
    316318when a large number of phases are associated with the event.  Also, as the 
    330332  The overall weight of a pick in the location process is the product of three 
    331333weighting factors: a phase-weight, a pick-quality-weight and a distance-weight. 
    333335     wt = phase-weight * pick-quality-weight * distance-weight 
    335337  The phase-weight is based on the phase assigned to the pick by binder, in 
    336338conjuction with the "ph" commands listed in the configuration file. Use 
    359361the distance-taper function set with the "taper" commands (see the "Residual 
    360362Tolerance Distance Term, dist-taper" section above): 
    362364  distance-weight = ((min dist-taper value)/(dist-taper value at r))**2 
    364366  The overall weight of a pick in the relocation process will be a number 
    365367between 0.0 and 1.0, inclusive. 
    368370plenty for most networks. 
    370 Relocation and Iteration Control: 
     372'''Relocation and Iteration Control''' 
    371373  Binder hands its locator a starting location and a list of phases. The 
    372374locator determines the pick weights as above, then calculates the event's 
    425 Post-Relocation Event Review: 
    426 Pick Culling, Pick Scavenging, and Killing Events: 
    427 -------------------------------------------------- 
     427==== Post-Relocation Event Review ==== 
     428'''Pick Culling, Pick Scavenging, and Killing Events'''  
    428430  Binder has just relocated an earthquake. Presumably, the location 
    429431is better contrained that it was before, and the arrival time fits 
    434436a series of tests. 
    436 Pick Culling: 
     438'''Pick Culling''' 
    437439  For each associated pick, binder compares the new travel-time 
    438440residual to the new residual tolerance value for that station (see 
    444446that event is sent back to the locator once again. 
    446 Pick Scavenging: 
     448'''Pick Scavenging''' 
    447449  After an event is relocated, binder also looks through its list 
    448450of recent picks to see if there are any others which may fit the 
    465467second event is also sent back to the locator. 
    467 Killing Events: 
     469'''Killing Events''' 
    468470  In reviewing events, binder sometimes decides that an event is 
    469471no longer valid, either because its location parameters are poor, 
    484 Quality Control: Pick-group Assessment 
    485 --------------------------------------- 
     486=== Quality Control: Pick-group Assessment === 
    486487  Occassionally one of binder's newly stacked events will include an 
    487488outlying pick which falls at a "leverage point" for the hypocenter 
    549 Examples from Binder's Log File 
    550 ------------------------------- 
     550=== Examples from Binder's Log File === 
    5515511. Stack: five picks stack to create a new event. 
    561 Trouble-Shooting 
    562 ---------------- 
     561=== Trouble-Shooting === 
    563563Binder's not producing any earthquakes - what could be wrong? 
    5655651. Is it seeing any picks? 
    566566   Check the log file, you should see some lines like these: 
    567568 10  6  3 2189 MWB  NCVHZ D2  19990930005310.08     431     672     584 
    56856919990930_UTC_00:53:15 grid_stack, mhit = 0 
    569571   The first line is a TYPE_PICK2K message, the second is the log of an 
    570572   stacking attempt.